EC (EC=electronically commutated) motors of the above referenced general type are sufficiently well known and are used for a number of applications. As is known, an EC motor is a permanent magnet-excited synchronous motor without a slip ring and is provided with a rotor position sensor and operated with a DC current via a commutation electronics unit (control and power electronics). This DC voltage can be provided as a DC link voltage by rectifying an alternating voltage from the power grid. As a function of the rotor position, the commutation electronics unit generates an AC voltage, in particular a three-phase AC voltage, from the DC voltage in order to generate a rotary field in the stator winding.
EC motors have many advantages. Because of their electronic commutation without a slip ring, neither brush noise nor wear occurs. These motors are therefore maintenance-free. Due to the electronic controller, additional functions such as stepless speed control, rotational direction reversal, soft startup and/or lock-up protection can be implemented without difficulty. The speed is generally adjusted by PWM clocking with an adjustable or controllable duty cycle.
For many applications there is the desire, based on economic and environmental reasons, to operate such EC motors with solar energy, this being by means of solar cell generators with a photovoltaic voltage.
For example, the document U.S. Pat. No. 5,493,155 A describes an electrical supply system for an electrical drive unit, for example a compressor for an air conditioning system or refrigerating machine, wherein a DC link is directly supplied via a rectifier from a grid voltage of a public supply grid. In addition, a solar cell generator (solar panel) is connected to the DC link, specifically via a controllable DC/DC converter, by means of which the photovoltaic voltage, which varies depending on the solar irradiation, is adapted to the DC link voltage provided by the rectified grid voltage. However, the DC/DC converter required in the solar circuit leads to an additional expense for circuitry and components as well as a reduced efficiency of the solar energy.